text: 
  exports.up = function (knex, Promise) {
      var default_channel = require('../app/database/defaults').channel;
      return Promise.all([
          knex.schema.table('channel', function (table) {
              table.json('previews');
          }),
          knex('channel').update({previews: default_channel.previews})
      ]);
  };
  
  exports.down = function(knex, Promise) {
      return Promise.all([
          knex.schema.table('channel', function (table) {
              table.dropColumn('previews');
          })
      ]);
  };
  